The present invention relates generally to managing water heater systems as a function of off-peak energy demand periods.
Just about every house, condominium, and apartment is connected to a water heater. A storage water heater typically holds about fifty gallons (190 liters) of water inside a steel reservoir tank. A thermostat controls the temperature of the water inside the tank. Many water heaters permit a consumer to set the thermostat to a temperature between 100.0 and 180.0 degrees Fahrenheit (F.) (thirty eight to eighty two degrees Celsius (C.)). To prevent scalding and to save energy, most consumers set the thermostat to heat the reservoir water to a temperature of around 120.0 degrees F. to 140.0 degrees F. (about forty nine degrees C. to sixty degrees C.).
The water heater usually delivers hot water according to the thermostat temperature setting. Consumers typically draw hot water in the morning to take a shower, in the afternoon to wash clothes, and in the evening to take a bath. As a consumer draws water from the water heater, the water temperature in the water heater usually drops. Any time the thermostat senses that the temperature of the water inside the tank drops too far below 120.0 degrees F. (forty nine degrees C.), the thermostat usually sends a signal to electric coils (or a burner in a gas water heater). The electric coils will then draw energy to heat the water inside the tank to a preset temperature level.
Most consumers do not spend much time thinking about their water heater until, one morning, they go to take a shower and there is no hot water. Another time they think about their water heater is when they receive their monthly bill.
Whether gas or electric, water heaters require a significant amount of energy to heat their reservoir of water. The cost for electrical energy can depend upon the time of day. In areas of the United States where energy is at a premium, utility companies often divide their rates into off-peak and on-peak energy rates based on off-peak and on-peak energy demand periods. Energy used during off-peak may cost the consumer in United States dollars around 2¢ to 3¢ per kilowatt-hour (kWh) while on-peak energy may cost anywhere from 6¢ per kWh to 50¢ or more per kWh. The utility companies eventually pass these extra costs on to the consumer. In a recent California energy crisis, the wholesale cost of energy rose to $3.00 per kWh.
Without some sort of management, a water heater that heats based on the water demand of a household most likely will heat when energy demand on a utility company is at its highest. Drawing energy to heat a water heater during these on-peak energy periods increases a consumer's monthly energy bill and, in the collective, places excessive wear on a energy generating facilities so as to shorten the overall life of the plant. In many cases, on-peak usage creates a cumulative energy demand that exceeds the capacity of the energy generating facility.
Many utility companies have off-peak water heating programs that provide lower energy rates. These lower energy rates apply so long as the consumer's water heater draws energy only during off-peak energy periods. A typical program provides for domestic hot water needs by heating a cooperative member's water during the off-peak energy periods. A clock timer attached to the water heater controls when the water heater will charge to 120.0 degrees F. (forty nine degrees C.). The charging period may vary for off-peak water heating, but typically lasts eight hours during a twenty-four-hour period. The eight-hour charge may come in a continuous block, or broken up into two-hour or four-hour time slots. There may be an additional two-hour charge period per day on weekends and holidays.
Off-peak water heating programs typically aid in reducing on-peak demand. However, to qualify for most off-peak water heating programs, the consumer must have at least 100 gallons of water heater capacity and have a clock timer attached to the water heater. The consumer typically will need to buy a new water heater to participate in the program. Moreover, there may be times during the on-peak energy periods when the consumer desires hot water, but the consumer's hot water heater is out of hot water. Here, the consumer may override the clock timer to obtain the hot water but will incur significant kWh energy charges. What is needed is a system that manages the heating of the water during the off-peak energy periods to supply needs of a consumer during the on-peak energy periods, to time-shift the demands on energy generating facilities, and to save the consumer money.